The present invention relates to microwave antennas and, more particularly, to microwave radiators for uniformly applying microwave energy to material conveyed past the radiator.
Heretofore, microwave applicators have been proposed which employ a broadside antenna to direct microwave energy onto material to be treated. Some such applicators have been complex structures comprising multiple waveguide radiative elements excited by loop coupling from a coaxial line. In addition to being expensive, these structures have been limited in power to the maximum power capability of the coaxial feed line, and, in use, these devices have encountered problems with energy reflection back to the antenna. Other applicators, e.g., U.S. Pat. No. 3,622,732 to Williams, have employed conductive enclosures such as multi-mode cavity resonators fed with microwave energy at spatially separated feed points to treat materials passed through the resonators. However, these devices have proven ineffective in providing uniform treatment of lossy materials because the energy distribution within the resonator becomes nonuniform when the material is introduced into the cavity, and difficulties have arisen with varying loads pulling the frequency of oscillation of the microwave tube causing high power reflections and poor efficiencies. Still other microwave applicators, e.g., U.S. Pat. No. 3,764,768 to Sayer, have employed an array of shunt slots one-half wavelength apart centrally communicating through one side of a rectangular waveguide, individual slots being provided with a slot loading member adjustable to vary the power coupled out through the slot and thereby affect a uniform output from the applicator along the length of the waveguide. However, this device has been found subject to the serious disadvantage that the slot spacing arrangements and slot loading members create impedance mismatches and cause energy reflections which result in power coupling inefficiencies.